It's not "simply injecting free loot," it's a reward-based system that would not only make hitting those pathetic 30k/30k bases viable (b/c those bases are smartly dumping all their gold AND elixir now into walls), but also provides you the opportunity to use more expensive armies if you choose to do so. As it currently stands, using anything other than BArch is insane if you're trying to stockpile resources. You slap a penalty to the league bonus multiplier similarly to how the current loot penalty exists, so that TH9/10s don't make their nut BArching TH7s for 3 stars in Crystal.
What it does is it helps solve the problem where the problems exists: higher TH level active players who are raiding other higher TH level active players. Currently they're just wasting their time b/c at that point in the game, they are smart enough know they should keep storages low, and with the elixir for walls update they can now dump both resources. A injection of loot is 1000% needed. Not necessarily with an increased collector level, which would be your "free loot injection," but a way where it needs to be earned. It's a direct response to the problems players are facing: players who bring armies capable of hitting storages but there is no loot in the storages. This league bonus multiplier serves as a safeguard where you don't bankrupt yourself simply b/c SC introduced a resource dump update without simultaneously installing a system that would account for the problems active players would face from it.

